The present invention relates to refrigeration and air-conditioning systems, and more particularly, to a method and an apparatus for controlling the flow of air through a transport temperature control apparatus.
Transport temperature control apparatuses are commonly mounted on refrigerated containers, refrigerated straight trucks, refrigerated tractor-trailer combinations, and the like to maintain cargo, such as foods, beverages, plants, flowers, and the like, at a desired set point temperature. In other applications, temperature control apparatuses can be used to condition air in a conditioned space to improve human comfort, such as for example, in buses and passenger trains.
Typically, conventional temperature control apparatuses include a heat exchanger, which extends into the conditioned space. An evaporator coil extends through the heat exchanger and is fluidly connected to a refrigeration circuit. In the refrigeration circuit, a refrigerant, such as for example, a chlorofluorocarbon (CFC) or a cryogen, is cooled, compressed, and/or stored. Liquid refrigerant from the refrigerant cycle is forced into an inlet in the evaporator coil. Warm conditioned space air is then drawn into the heat exchanger through an air inlet and is blown across the evaporator coil by a fan or blower. The relatively warm conditioned space air contacts the relatively cool evaporator coil and is cooled thereby before being forced back into the conditioned space via a discharge in the heat exchanger. The refrigerant is then directed out of the evaporator coil and may be re-compressed and re-cooled in the refrigeration circuit to be recycled through the evaporator coil.
Occasionally, water vapor from the conditioned space can be separated from the air and can condense on the evaporator coil, forming frost. To minimize the formation of frost on the evaporator coil and to remove frost from the evaporator coil, conventional temperature control apparatuses periodically operate in a defrost mode. In the defrost mode, hot gases are directed through the evaporator coil to heat the coil and melt any frost that may have accumulated on the coil. Alternatively, electric heating elements can be used to heat the air in the heat exchanger. To prevent unnecessary heating of the conditioned space, air is not directed through the heat exchanger during operation in the defrost mode. In defrost, airflow is typically restricted using a damper to close the discharge while the fans continue to operate.
According to the present invention, a transport temperature control apparatus operable in a cooling mode and a defrost mode includes a refrigeration circuit and a heat exchanger having an air inlet and an air outlet. The air inlet and the air outlet are in fluid communication with a conditioned space. An evaporator coil extends through the heat exchanger between the air inlet and the air outlet and is fluidly connected to the refrigeration circuit. A divider is positioned substantially perpendicular to the evaporator coil and defines a first portion of the evaporator coil and a second portion of the evaporator coil. A first fan is housed in the heat exchanger and is positioned adjacent the first portion of the evaporator coil. The first fan has a first operating condition for directing air across the evaporator coil in a first direction and a first non-operating condition. A second fan is housed in the heat exchanger and is positioned adjacent the second portion of the evaporator coil. The second fan has a second operating condition for directing air across the evaporator coil in a second direction and a second non-operating condition. The second direction is opposite the first direction.
In some embodiments, a damper is positioned in the air discharge for selectively preventing air from flowing through the air outlet and a heating element is positioned in the heat exchanger. The heating element can include an electric heater and/or a heating coil.
A controller is in electrical communication with the first fan and the second fan. The controller alternately operates the first fan in the first operating condition and the first non-operating condition and the second fan in the second operating condition and the second non-operating condition. The controller operates the first fan in the first operating condition for a first predetermined time and the second fan in the second non-operating condition for the predetermined time and then operates the second fan in the second operating condition for a second predetermined time and the first fan in the first non-operating condition for the second predetermined time. Also, the first and second fans alternately direct air in the first direction and the second direction.
The present invention also includes a method of conditioning air in a conditioned space with the transport temperature control apparatus. The method includes operating the temperature control apparatus in a cooling mode. The cooling mode includes directing air into the heat exchanger through the inlet with the first and second fans, transferring heat from the air to the evaporator coil and directing air out of the heat exchanger through the discharge with the first and second fans. The method also includes operating the temperature control apparatus in a defrost mode. The defrost mode includes activating the first fan and deactivating the second fan. The first fan directs air in a first direction across the first portion and then across the second portion. The defrost mode further includes activating the second fan and deactivating the first fan. The second fan directs air in a second direction across the second portion and then across the first portion. Additionally, the defrost mode includes heating air in the heat exchanger with a heating element positioned in the heat exchanger.